The present invention relates to a synchronous motor driving apparatus which controls a synchronous motor without using a sensor for detecting an electrical angle position.
There are proposed a lot of methods of presuming an internal magnetic pole position of a synchronous motor to control the synchronous motor without detecting an electrical angle position of a rotor. For example, Japanese Patent Publication JP-A-2002-78392 discloses that voltage pulses are applied to a permanent-magnet synchronous motor (hereinafter referred to as PM motor) in two orthogonal-axis directions to detect amplitudes of current pulses generated in the respective axial directions and presume a magnetic pole position. In this method, an approximation equation showing the relation between the generated currents and the presumed magnetic pole position is introduced to thereby minimize the number of times of application of the voltage pulses, so that the accuracy of the presumption is ensured.
Further, Japanese Patent Publication JP-B-8-13196 (JP-A-3-207250) discloses that positive and negative voltage pulses are applied to three phases to detect amplitudes of current pulses generated in the three phases, so that the magnetic pole position is presumed on the basis of the detected amplitudes. In this method, the accuracy of presumption is limited to the range of ±30 degrees but detection of the current pulses is easily attained by detecting DC current of a power converter.